The present invention relates to high pressure intensifiers.
Within the subsea oil industry, subsea trees require few high pressure valve functions. For most wells, often only one high pressure valve, typically the subsea safety valve (SSSV), is required on each well head tree. This valve requires a source of high pressure hydraulic fluid at the seabed. The cost of an additional high pressure line in an umbilical from a surface platform to a well is very expensive, so subsea pressure intensification, local to the well tree, is sometimes used. This is particularly cost-effective when a number of wells are strung out as offsets fed from a primary manifold, especially as the offsets are increasingly further away from the manifold. Where subsea pressure intensification is used, a high pressure accumulator is designed into the system and, since the SSSV is operated extremely infrequently, the intensifier is only required to top up the accumulator.
Current subsea intensifiers are highly engineered, and can be expensive and unreliable. Typically, they are self-governing, twin-acting, intensifiers that rely on a piston reaching the end of its stroke to trigger a change-over valve, to send the piston back in the opposite direction. When the high pressure fluid demand is almost zero, i.e. when the SSSV is not being actuated and only fluid leakage is ‘consuming’ pressure, the piston can stall at the end of the stroke with the change-over valve in a half-moved position. In this condition, these devices leak from a low pressure supply, to a return. This can compromise the function of the field and the change-over valve concerned can only be unstuck by actuating the SSSV to ‘consume’ some high pressure fluid. The SSSV is functionally critical to the oil well and can not easily be replaced if it wears out. This invention enables an improvement, which is more reliable, cheaper and more error tolerant in engineering.
GB-A-2 461 061 describes an intensifier using directional control valves (DCVs). Other forms of hydraulic intensifier are described in GB-A-2 275 969, EP-A-0 654 330, GB-A-2 198 081, GB-A-1 450 473 and EP-A-1 138 872.